Control apparatus for molding presses



Dec. 7, 1948. J, TAUBER ErAL 2,455,823

CONTROL APPARATUS FOR MOLDING PRESSES F lg. l.

JNVENTOR.

John A. Tcuber 5 Harold A. Heiligmun A TTOR/VEY Dec. 7, 1948. J; AITAUBER ET AL 2,455,823

CONTROL APPARATUS FOR MOLDING PRESSES Filfid larch 3, 1.948 I 5 ShGOtS-Shflqt 2 X Fig. 5.

INVENTOR. John A. Tquber y Harold A. Heiligmon WW ATTORNEY J\ A. TAUBER ETAL CONTROL APPARATUS FOR MOLDING PRESSES Dec. 7, 1948.

5 Sheets-Sheet 3 Filed March 3, 1948 INVENTOR.

John A. Tauber Harold A. Heiligmon WW -Md ATTORNEY 1948- J. A. TAUBER ETAL 2,455,823

CONTROL APPARATUS FOR MOLDING PRESSES File g F011 3, 1948 5 Sheets-Sheet 4 r7 we r 1 I a m i l F 35} l 38 /84 F- J J JNVENTOR.

John A. Tuuber y Harold A. Helligmon q- 4 mm A TTOR/VE Y 7, 1948. J, TAUBER ETAL 2 455 3233 CONTROL APPARATUS FOR MOLDING PRESSES Filed. March 3, 1948 5 Sheets-Sheet 5 Pressure on Brick Form Time v INVENTOR.

John A. Tuuber Fi a g By Harold A. Heiligmon g. I I m A TTORNE) Patented Dec. 7, 1948 CONTROL APPARATUS FOR MOLDING PRESSES John A. Tauber and Harold A. Helligman, Norristown, Pa., assignors to E. J. Lavino and Company, Philadelphia, Pa., a corporation of Delaware Application March 3, 1948, Serial No. 12,812

12 Claims. I

This invention relates to a control or regulator apparatus, and method of using the same, for molding presses. More particularly it relates to apparatus or devices for controlling the volume of the material fed into the molds of a molding press such as a brick press during the feeding portion of the brick-forming cycle.

In a brick press, especially of the type known as the Boyd press, an example of which is shown in the patent to Flood No. 987,124, there is provided a mold with plungers to form the top and bottom of the mold. Means are provided for supplying material to the mold, and motor driven means are provided for moving the plungers toward each other for thus pressing the material in the mold into the shape of a brick. In a press of this general type, the position of the bottom plunger at the time the mold is filled determines the volume of the brick-forming mix which enters the mold, and therefore, determines the forming pressure, the weight of the brick, the thickness of the brick, and influences to a large degree the porosity and densityof the brick.

The manufacturer of bricks, especially refractory bricks, strives for uniformity in the thickness, Weight, and qualities of his product. The density and porosity of refractory bricks greatly influence several refractory qualities in which uniformity is an essential factor such as slag absorption, chemical reactivity to furnace slags and furnace atmospheres, and resistance to thermal shock. Uniformity of the bricks in the pressing operation is dependent upon three factors, the time of each pressing cycle being constant: (1) uniformity of the volume and the apparent density of the brick-forming mixture entering the mold during each cycle; (2) the same position of the bottom plunger relative to the top of the mold during each mold-filling operation; and (3) the application of the same amount of pressure during each cycle. Since the commonly used method of feeding the mold does not provide for absolute uniformity in the density of the brick-forming mixture entering the mold on each cycle, it is necessarythat means be provided for making volume adjustments by controlling the position of the bottom plunger to compensate for variations in the density of the brick-forming mixture. In

the normal press operation the adjustment is made manually from time to time, some times every few minutes, by the operator who judges from the weight and thickness of the brick whether the proper amount of material has been used, or from the sound of the press (as learned from his experience) whether excessive pressures are being used in brick-forming. I

The adjustment of the volume of the mold to compensate for variations in the density of the brick-forming mixture also results in greater uniformity of the pressure xerted by the press on the brick-forming mixture from cycle to cycle.

The operator is then able to effect the adjustment by turning a handwheel either in the one or in the other direction whereby he either raises or lowers the normal position of the bottom plunger relative to the mold by degrees according to his empirical judgment. The handwheel turns a screw spindle having a suitable 1ost-' motion operating connection with the bottom plunger of the mold.

Objects of this invention are to provide a eontrol apparatus for molding presses to effect automatic variation of the volume of the material entering the mold in a manner to compensate for variations in the apparent density of the brickforming material, and to effect adjustment of the weight of the material entering the mold of the press during the mold-filling portion of the cycle, in order to maintain substantially uniform pressure peaks from cycle to cycle by using the peak pressure of a preceding cycle to regulate the peak pressure reached in the succeeding cycle.

A known manner of making such adjustments is to make use of means for adjusting the initial or normal position of at least. one of the plungers to vary the effective depth of the mold, which includes a reversible motor and means for automatically controlling the direction and extent of motion of the reversible motor.

Therefore, this invention may be said to constitute an improvement over the patent to Yeakel No. 2,256,798 in which automatic control of the brick-forming volume is governed by the electric peak power demand of the pressure during the brick-forming cycle. In this patent the peak power demand if excessively high starts a reversible motor which relatively raises the bottom plunger of the brick-form so as to decrease the effective mold volume. Correspondingly a peak power demand that is excessively low starts the reversible motor running in the opposite direction thereby. eifecting a relative lowering of the bottom plunger so as to increase the effective mold volume. In this Way the volume of the brickforming material is decreased or increased, as the case may be, in response to density variations of the material, although the mold volume during the same. Thus the dimensions of the bricks produced are uniform although density variations are being compensated tor.

The present invention provides improved means for the automatic controlled variation of the brick-forming volume.

In order to attain the above objects this inventlon proposes to utilize the mechanical stress or elastic strain imposed upon certain parts of the press by the peak pressures of the brick-forming cycle as a criterion and to translate or convert that strain into an impulse for effecting corrective control of the volume of the brick-forn1ingmixture being fed to the mold in each cycle.

This invention utilizes the peak pressure strain or stretch or elongation imposed upon those parts of the press structure which most directly absorb the peak pressure. Thus in the case of the aforementioned Boyd press this invention utilizes the strain or stretch imposed upon the side bars of the vertically movable frame herein also termed the sub=frarne that carries the top and bottom plunger ofthe brick form or mold.

The strains are such as to result in elastic deformation 'or stretching of the respective structural parts in the sense that the stretch or elongation of the part or parts is directly proportional to the stress or load imposed upon them. This elongation is called. elastic for the reason that it disappears when it is relieved of the load. Hence, a peak brick-forming pressure is characterized by a proportionate temporary or momentary peak elongation of the respective structural parts. Such elongations are extremely minute and are defined for various materials by their respective moduli of elasticity, that is the figure or factor that indicates how much a material. under load will stretch within its limits of elasticity. For example, steel has a modulus of elasticity of 30,060,000 which means that a load of one pound imposed. parallel to the length of a bar having a cross-sectional area of one square inch will produce a change in length of one thirty-millionth of an inch per inch of length of the bar. In recent years such inflnitesirnally small elastic deformations or elongations, for example of steel or other materials have been rendered more conveniently measurable by. means of electronic devices. In principle and in simplified form one such device comprises as an initial or primary ele ment, the so-called strain gauge of which there are several types available but which will herein be exemplified by a resistance type strain gauge, that is a minute filament carrying an electric cur= rent and suitably attached or bonded to the part that will be subjected to the elastic elongation. In this way the strain gauge or resistance filament will be subjected to compression or elongation concurrently with the structural part under stress. The resistance of the strain gauge is thus altered in accordance with the degree of elastic structural deformation. This minute change of resistance in turn is registrable by suitable electronic tube devices which may translate or relay or amplify the impulse thus received into indications or relayed control actions. In principle, therefore, an electronic amplifier tube or electronic valve may serve this purpose.

We attain the objects of this invention by electronically relaying the mechanical strain or elas ,tic elongation of the sub-frame caused by the peak brick-forming pressure, into automatic relay actions which efiect corrective adjustments of the brick form volume or else of the brick-forming forming peak pressure occurs it will set into m0- tion a corrective or compensating action towards eflecting an appropriate decrease in the effective volume of the brick mold. If an excessively low brick-forming peak pressure occurs, it will correspondlngly produce an instantaneous impulse towards effecting an appropriate increase of the effective volume of the brick mold.

The Boyd press as such is well known and is a complicated and powerful machine, but since this invention relates to auxfllary or control equipment there will herein only be shown and described those parts of the press which are believed to sumce for a general understanding of its operation and to furnish the environment for the controls to be applied to the machine according to this invention. I

Such a press comprises a. main solid vertical machine frame in which a secondary frame or sub-frame is vertically guided and resiliently supported as by means of compression sp s and is therefore herein also termed the floating subframe or floating frame. This sub-frame consists of vertical side bars rigidly interconnected by transverse topand bottom end members. The sub-frame in efiect carries the brick-presslug mechanism proper. This mechanism comprises an upper plunger unitary with a cross-head which is vertically guided in the sides of the subframe and vertically reciprocable through the action of a. pair of toggle links or members suspended from the top end of the sub-frame and in turn actuated by the horizontally reciprocating motion of an eccentri driven pitman connected to the intermediate articulation point of the toggle links. Thus the upper plunger or cross-head will vertically reciprocate because of the horizontal reciprocation of the intermediate articulation point of the toggle links.

The pressing mechanism also comprises the bottom plunger which is unitary with the so-called saddle that is a. member which is yieldingly mounted and supported upon the bottom end of the sub-frame an resiliently depressible thereon. Hence the bottom plunger is capable of downward movement against spring pressure from its normal position relative to the sub-frame. This upwardly spring-urged normal position of the bottom plunger may be subjected to adjustments, whereby a lowering or downward adjustment will cause a commensurate increment of spring compression, while 2. raising or upward adjustment will cause a commensurate degree of tie-compression of the spring. Such are the adjustments to be effected automatically in response to peak pressures by the improved control devices of this invention.

Both the top and the bottom plunger cooperate with the vertical walls of the brick form or mold, as provided by a stationary mold table or loading platform which is rigidly unitary with the main stationary frame. That is to say, after the mold has been filled the top plunger enters the mold pressing the brick-forming mixture, the maximum or peak pressure being reached approximately at the bottom of the down-stroke of the top plunger and being maintained for a. short period of time as the bottom plunger starts its upward stroke. Then both the topand bottom plungers move upwardly maintaining approximately their relative positions until the bottom plunger reaches the top edge of the mold. The upward stroke of the bottom plunger terminates at the top edge of the mold while the top plunger continues its upward travel to a position which provides clearance for sliding or removing the finished brick onto the table or platform from the press, and to allow a charger or mold-feeding box to pass horizontally over the mold for re-charging the same. After the brick has been removed from the press, the bottom plunger returns to the position at the bottom of the mold, and the top plunger remains stationary as the charger refills the mold. The charger or feeding box then withdraws horizontally leveling the excess loose material even with the top of the mold or loading platform, whereupon the brick-forming cycle is repeated. The coaction or functional coordination of the top and bottom plungers with respect to each other and with respect to the mold charger is effected through the medium of suitable levers and toggle members motivated from the main press-operating motor. The bottom plunger is reciprocated in the proper rhythm by reciprocation of the sub-frame through such master-controlled means or mechanism. Such actuating means are well known in the Boyd press and are not particularly shown herein.

In the operation of the press the reciprocating charger has the dual function of feeding the mold and of delivering the brick onto the platform or table. The topand bottom plunger disposed opposite one another fit the mold and act upon the material placed therein by the charger. In the course of a brick-pressing cycle both plungers compress the material in the mold, then the upper plunger withdraws upwardly while the bottom plunger advances to lift the resultant brick out of the mold and to the level of the mold table, whereupon the advancing charger delivers the brick onto the table and simultaneously refills the mold. After the charger has been withdrawn the brick-forming cycle starts anew. Thus, when the toggle members straighten out, bringing the top and bottom plungers toward each other, they exert pressure to compress the brick-forming mixture contained between them and confined by the vertical walls of the brick mold, and this pressure for its duration imposes an elastic stretch or elongation upon the side bars of the sub-frame. Measurement of the extent of this elongation, also termed strain, provides a measure of the absolute brick-forming pressure. This measurement, according to this invention, can be utilized as an impulse to operate a reversible auxiliary motor such as disclosed in the aforementioned Yeakel Patent No. 2,256,798 to effect the corrective control of the mold volume.

When the position of the bottom plunger during the mold-filling portion of the cycle is properly adjusted, that is to say when variations in the apparent density of the brick-forming mixture are compensated for by controlling the volume of the mold, the pressure values indicated by the side bar strain of the sub-frame are' substantially uniform. Measurements of hundreds of bricks made under conditions in which the side bar strain was uniform show that under those conditions the bricks are more nearly uniform in thickness, weight, and density. By the present invention there is provided a control or regulator apparatus in which variations from 'a chosen value for the side bar strain automatically actuate means which increase or decrease the volume of the material fed to the mold to correct the condition which caused the variation.

Features of this invention reside in the electrical circuits effecting the control, and certain dispositions of the strain gauges within the electrical control system,

According to one feature strain gauges are so disposed within the electrical system that a variation of their resistance due to temperature changes is compensated for.

That is, each side bar of the sub-frame is provided with a pair of strain gauges, the one gauge being applied in the direction of load application strain and thus subject to elongation when the load is applied, the other being applied transversely to the direction of load application and thus being subject to compression when the load is applied. The compression experienced by the transversely applied gauge will be very much less than the elongation experienced by its companion gauge. Both pairs of strain gauges are connected into a Wheatstone bridge circuit in such a manner that the temperature factor is compensated for. When due to strain in the sub-frame the bridge system becomes unbalanced, the resulting bridge circuit is utilized through electronic relay action to start the reversible auxiliary motor in the sense of rotation that will produce the required adjustment of the bottom plunger.

According to another feature, control switch means are provided which are governed or timed by the operation of the press in such a manner that the electrical control system is placed under the controlling influence of the Wheatstone bridge only during that phase of the press cycle which substantially represents the duration of the peak pressure, that is the phase within which the corrective adjustment impulse is to be relayed due to unbalance of the system. During the remainder of the cycle the control system is kept in balanced or neutral condition due to its being connected to an auxiliary constant voltage source. That is to say, the control system is kept electrically alive or primed although balanced in neutral during the offor rest period, that is the periods prior to and after the peak pressure appears.

According to a more specific feature, additional switch means are provided and governed by the operation of the press, and timed with respect to the first-mentioned switch means in'such a manner that the operation of the auxiliary motor is eil'ected during a period that lies well within the peak pressure period during which the Wheatstone bridge is connected to the control system proper.

Therefore, in terms of electrical control phases the cycle may be defined as comprising:

1 (a) an offor rest period before and after the peak pressure occurs, during which the control system proper is kept in neutral balance due to its connection to an auxiliary constant voltage source, thus to condition the system for subsequent connection to the Wheatstone bridge,

(b) an alert period which within the cycle is complementary to the oil-period, and during which the control system proper is placed under control of the Wheatstone bridge circuit for the pro-determined duration of the peak pressure phase, thus to condition the system preparatory to realizing the adjustment proper through the auxiliary motor; and

' (c) the active control period which falls well within the alert period, and therefore represents only a portion of that' phase, during which the auxiliary motor is actuated to make the adjustment to the extent dictated by the bridge circuit.

Thus a required total adjustment of the botoneness toni plunger may be music piece neel during the active control period of as number of consecutive press cycles until the clemancl oi the Whentstone bridge is satisfied.

More specific features lie in the operation oi the master switch means or timing switches which govern the above phases oi the control cycle, and in the manner of their application to the press. a

The invention. possesses other objects oncl ieo= tures of cdvantose, some of which with the lore going will be set forth in the following clescrip= tion. in the following description and in. the claims, parts will Toe identified Toy specirlc names for convenience, but they ore intended to be as .geneuc in their spplicetion to similar ports es the will permit. In the accompanying drawings has been illustrated one embodiment of the int tion, but such embodiment is to be regsrclecl typical only of possible embodiments, end the invention is not tobe lirnltecl thereto.

novel features considered characteristic cl our invention are set lorth with particularity in the appended claims. The invention itself, how= over, both as to its organization oncl its methocl oi operation, together with sclrlitionsl objects and nrlventeges thereof, will best be understood irorn the following description or e. specific embocli= when read in connection with the sccorn= l is e. semi-diagrammatic sectional side of e press of the Boycl type;

i. 2 is s semi -diagrammatic sectional front view of the press shown in i, showing mo e ly the vertical movable sub-ironic within the nary main machine frame, as well es the tion upon the machine of master con witches governing the adjustment of the volume 05. the bricloforrning mixture for och brick-forming cycle;

3 is o diagrammatic side view of the sub fro. ie showing the relative disposition of a pair of sin gauges relatives to each other and relo= tive to the vertical direction of stroin in the solo frame;

Fig. is o Wiring diagram of the electrical con= trol system through which strein indications in the sub-frame are translated into corrective ecliustrnents of the bottom plunger oi brick :Zorin, varying the feecl volume of the hricir=Liorm= ring mixture in accordance with voriations in the so cut density of the mixture;

. 4 shows an enlarged end portion of the s wiring diagram;

5 to are oletell views of the muster control switches governed directly by the press, in various operational positions of the cycle;

ill is a suit-detail view somewhat reduced of a. part of Figs. 5 to 10;

Fig, 11 is a chart of the bricls=f0rlming cycle in terms of briclbforming pressure as a. function of time, indicating the timing of the rooster control switches with respect to the peel: briclrolorming pressure as well as with respect to each other.

A brick press of the Boyd type as shown in scmi-cllsgrammotic fashion in Figs. 1 and 2 comprises a stationary machine frame it in which there is vertically sliclable a sub-frarne ill horizontally supported upon the main frame as by springs 82 and i3 disposed one at each side of the sub-frame. The sub-frame consists of e. pair of side hers it and it) rigidly interconnected at the top by a transverse member or heed-end or pivotal member It, and at the bottom by e. transverse member or foot-end portion or'bearn ill.

iii

Ell

' i8 is in. its lowest The sub irsme ii in effect carries the entire brick-forming mechanism-proper including o toi plunger i8 and is bottom plunger it) cooperating with the verticoi wells of the stationary loricl: lorrnproper 26 which is proviclecl in a loading platform or worlr=teble 2i rigidly carried by the mochine home. While this description species or top plunger nncl bottom plunger constituting the top one bottom respectively oi t e brick form, it will unclerstoosl thot the Boyd type press employs o. plurality oi brics forms, and hence e. plurality of top plunger-s with u correspending plurality of bottom pioneers, ell forms working in parollel simultaneously. For the seize oi simplicity, the following" description oi the machine and operstion will substen tinily only to one brief. form with one top and one bottom plunger.

Each plunger tlsrecl to its outer or brlcls en gecing encl c or she piste that into the brick form, so the hriclz: is conipresecl between the the plates while being confines]. by the vertical walls oi the brici: form surrounding thorn. Thus the top plunger hos mold-engaging die it, and the bottom plunger i9 o molchengeging rile ill The upper die is ri ly ottochecl or unitary with e. cross-heed suiclerl for vertical movement in sub trscie i i, its up-snrl clown move ment losing control ed by or vertical toggle members or links curl fi l the upper toggle linlr 2i] swinsehle about the upper trons verse member or pivotal member to oi the sub frame. Both toggle links onsl 2G ore inter connected hy woy or culotion inclicotecl by e pivotal member to which is uttechecl o plt= mun ill reciprocoteii by on eccentric pivot on cronlr 2&3 prcvicletl crank shaft or rosin press shalt 29 which is customary clrive means as inches-teal filled on crsnlr shalt pinion mounted on sheit 3i drives gear A helt driven pulley es mounted. on c.- shsl't through suitelole ririve scoring (not visibl in it drives These clrive moons being no of this invention are described in niorernentionecl patent to Flood No. 987,12.

Within o bricleior cycle the top plunger ermine position when the toggle linlzs 2S 2G ore straightened or in vertical dead center position; whereas when the toggle linlzs are in their ofhcleou center position, top plunger will hove reochecl its highest position clear of one. roisecl e. clists'nce above the brlcls iorrn. oresent mechanism suchthe plungers p alfirlll single brie forming operation n e. complete revolution of the cronis shsit The bottom plunger 50 is mounted upon and fixed to what is herein termed e souclle 3&3 which is vertically movable and resiliently clepressible' upon and with respect to the lower transverse member or beam i'] all sub-frame ii. That is to say, the saddle 823 is urged upwortily from the bottom portion oi the sub-frame by a compression spring 36 confined between the ssclclle 33 end the lower encl of the sub frsnie ii. The degree of initial compression of this spring lit determines the initial brick-forming position of the bottom plunger it in the brick-forming cycle, that position, however, being adjustable by e handwheel 35 by means of which an operator can rotate a vertical screw spindle mounted in a stand 31.

the spindle 38 will raise or lower a nut 38 upon the lower end portion of the spindle. Thus nut 39 while capable of being raised or lowered relative to the stationary machine frame is held against rotation by its sliding-or block-and-slide engagement with the double-armed lever 39 the forked ends 49 of which engage upon lugs 4i and 4| provided upon the nut 33. That is, the lugs 4| and 4| lodge in slots formed by and between forked ends 40. The'lever 39 is fulcrumed at with a cross-bar to which are connectedrods 4! extending upwardly and being concentric with and surrounded by the springs 34, the upper ends of these rods being connected with the saddle 33.

The lower plunger I9 is held in itsinitial brickforming position by the'lever 39 engaging thecross-bar 44, although in the further course of the brick-forming cycle the bar 44 disengages from the lever 39 as the bottom plunger l9 yields to the brick-forming pressure applied by the top plunger. Such manual adjusting means for the bottom plunger of the Boyd press is clearly shown in a perspective view in the aforementioned Yeakel Patent No. 2,256,798.

It will be understood in the course of the following description that the brick-forming cycle of the press is the result of the coaction of movements of plungers I 9 and I9 relative to the subframe I I, and of the movements of the sub-frame ll carrying the plungers relative to the machine frame.

During each the mold 20 in a known manner suitably controlled by the machine in correlation to the plunger movements by the mechanism embodied in the Boyd press but herein not specifically shown. Suffice it to say that a mold-feeder or charger or dispenser 48 receives its mold feed charge from a stationary feed hopper 41 and is reciprocated horizontally so as to slide upon the loading platform 2|. In the course of such controlled reciprocation the charger 49 receives its charge from the feed hopper 41 above it while in its extreme retracted position, and drops its charge into the mold below it after having been slid out from under the hopper to its extreme advanced position above the mold. The charger 49 is dimensioned to carry to the mold a dispensed quantity of material somewhat larger than the mold volume requires, and on its retracting stroke returns the surplus material leaving the mold content level with the platform and ready to be compressed by the subsequently descending top plunger I 9.

Hence, the brick-forming cycle of the Boyd press operates as follows:

Mechanism which is functionally assoc ted with the press holds the bottom plunger I initially in a predetermined adjusted position whereby the plunger constitutes the bottom of the mold 29 and defines the volume thereof to be filled by the brick-forming material. This material being supplied from the feed hopper 41 is loaded or falls into the mold-feeding box or charger 48 which has a capacity greater than that required to fill the mold. The mechanism moves the charger 46 to the dotted line position 48' over the mold, allowing its charge of material to dis charge into the mold. The charger is then returned to its loading position under the hopper, and on this return movement levels the excess loose material even with the top edge of the mold. The press mechanism then straightens the toggle links 23 and 24 and thereby lowers the top plunger I brick-forming cycle the brickforming material or mixture is fed or dispensed to ill) ll allowing it to enter the mold so as to press the brick-forming mixture therein. In compressing the mixture on its downward stroke .the top plunger also depresses the bottom Dlunger' against the pressure of the saddle spring. 34. Thus the maximum pressure is maintained at or about the lower dead-center position of the top plunger, and is also maintained for a short time as the bottom plunger l9 starts it upward stroke. As the top plunger continues upwardly, both plungers maintain approximately their relative positions with the compressed brick material between them, until the bottom plunger [9 reaches the top of the mold. That is to say. during the brick discharge phase of the cycle the press allows the lower plunger to rise past and above its initial mold-filling position until its top face is level with the face of the loadingplatform or top edge of the mold. Thus, the upward stroke of the bottom plunger i9 is stopped when the top face of the plunger is level with the face of the loading platform, while the top plunger l8 continues its upward travel to a position which provides clearance for the charger to slide or remove or displace the now exposed brick from the press as the charger passes again from its charge-receiving position under the hopper to its moldfilling position over the mold. This is to say, after the brick has been removed from the press the bottom plunger returns to its initial adjusted position at the bottom of the mold, and while the top plunger remains stationary in its raised position. the charger again proceeds on its outwardstroke to fill the mold, then to be withdrawn. whereupon the brick-formin cycle is repeated.

With respect to the pressure conditions occurring during the brick-forming cycle, it should be understood that the pressure exerted upon the brick-forming mixture by the top Plunger IS on its downward stroke into the mold causes the bottom plunger l9 which is fastenedto the saddle "3 to move until the saddle 33 touches the lower end or beam I I of the sub-frame ll compressing spring 34. The downward movement of the saddle 33 lowers the saddle rod 45 and its crossbar 44 so that the cross-bar no longer maintains contact with the pressureor mold volume-ad- Justing lever 39. The function of the mechanism is such that the pressing mechanism as far as it is mounted on the sub-frame ll then rises bodily with the sub-frame II in relation to the stationary press frame l9 although the top plunger i9 is still moving downwardly toward the ascending bottom plunger l9 causing maximum compression of the brick-forming mixture when the top plunger l3 and'the bottom plunger 19 are closest together. Mechanism for thus timing the vertical movement of the sub-frame ll relative to the brick-forming movements of the plungers l9 and I9 is part of the mechanism of the Boyd press but not shown herein.

After a brick was pressed in this manner, if

previously an operator of the machine wished to vary the volume of the brick-forming material passing into the mold for the next cycle he would turn the handwheel 35 to operate the pressureadjusting screw spindle 36. Turning the handwheel in one direction would lower the nut 38 on the spindle which in turn would depress the outer end of lever 39 by means of the lugs 4| and H engaging the lever. Thus the lowering of the nut 39 causes the inner end 43 of the lever to rise so that at the completion of the next downward stroke of the beam H or sub-frame II the position of the bottom plunger l9 will be raised since the contact of the inner end of lever 3| with .the cross-bar 44 has been raised. This in turn permits the mold 20 to receive a smaller volume of the brick-forming material from the charger ll. Hence, the result of this adjustment is that diminished pressure will be exerted by the plunger upon the material being molded, thus producing a brick that has been less strongly compressed, or that has undergone a somewhat lower peak pressure in the brick-forming cycle than the brick that preceded it.

If, however, the operator turned the handwheel 35 in the opposite direction, a reverse sequence of events would take place, resulting in an increase of the volume of the brick-forming mixture or material entering the mold, and in a higher peak pressure in the brick-forming cycle.

To effect mold volume adjustments automatically, this invention utilizes an auxiliary reversible motor for rotating the adJusting screw spindle .38 either in the one or in the other direction as the demand may require. Such a motor is indicated at 48 and is adapted to drive the spindle 88 through reduction gearing indicated at 40. The disposition and use of such a motor in connection with the previously handoperated spindle is shown in the aforementioned patent to Yeakel No. 2,256,798.

The Connor. SYSTEM (a) The master control switches There will now be described the automatic electrical control system proper of this invention whereby the auxiliary motor 48 is actuated to make the proper mold volume adjustments in response to peak brick pressure strains imposed upon the side bars It and It of sub-frame N. This control system will therefore be described in relation to the pressure-time diagram (see Fig. 11) of the brick-forming cycle. The control system itself is represented in the wiring diagrams of Figs. 4 and 4- and includes strain gauges A1. D and A2, D2 fastened to the subframe H (see Figs. 3 and 4) in a suitable manner to be unitary therewith, as well as master control or timing switches T1 and T: actuated by the main or crank shaft 28 (see Figs. 2 and 4, as well as detailed Figs. 5 to 10). The strain gauges may be said to represent the primary control elements of the system and comprise a pair of strain gauges A1 and D1 fastened upon one side bar of sub-frame II and a similar pair of strain gauges A: and D: fastened upon the other side bar of sub-frame H. It should be noted that the strain gauges A1 and A: are vertically disposed, that is co-extensive with the direction of strain occurring in the side bars due to the brick-forming pressure so that these strain gauges will have their resistance increased in proportion to the strain or elastic elongation imposed upon the side bars of sub-frame II by the peak brick-forming pressure. therefore herein be called the pressure-responsiveor simply responsive strain gauges. By contrast the strain gauges D1 and D2 are horizontally disposed. that is transversely of the direction of strain occurring in the side bars so that their The strain gauges A1 and A: will electrical resistance will remain largely unaifected by the strain in the side bars. The strain gauges D1 and D: will therefore herein be called the non-responsive strain gauges. To some extent strain gauges are susceptible to temperature changes varying their resistance. Since the proper or faultfree operation of a control system according to this embodiment requires that the absolute values of the strain indications remain substantially unchanged, there are herein provided compensating means wherebylndicating errors that might be due to temperature changes are cancelled out. This compensation for error is herein effected by a manner of associating the two responsive gauges with the two which are non-responsive, namely by associating them within a Wheatstone circuit W the arrangement and operation of which within the electrical control system will be described and explained further below. Each of the timing switches'Ti and Ta comprises a rotary double track cam member of non-conductive material upon the periphery or cam face of which ride a pair of stationary contact fingers when the cam member is being rotated. That is to say, each cam member is associated with a pair of resiliently flexible contact fingers each of which rides upon one of the peripheral tracks or cam faces of the cam member and engages them under a suitable contact pressure the magnitude of which depends upon the degree of resilient deflection of the fingers. The two cam faces or tracks of each cam member are so shaped and so disposed with respect to each other that during the rotation of the cam member they will cause the associated pair of contact fingers to make or break contact between them. In fact each cam member comprises a pair of disc-like component members or discs held together face to face, each of which discs represents a respective track or cam face of the cam member. The two component disc members may be rotatably adjusted with respect to each other in order to adjust the timing of the opening and closing of the contact fingers.

The rotary cam members of both switches T1 and To are fixed coaxially upon a horizontal axial extension 50 of the main press shaft or crank shaft is (see Fig. 2) so that each revolution of the cam members corresponds to a concurrent brick-forming cycle of the press. Hence, the function of the switches T1 and T: (shown in Fig. 2 as well as Figs. 5 to 10) will be more clearly understood when considered in its relationship to the pressure-time diagram of Fig. 11.

According to Figs. 5 to 9 the switch T1 comprises a rotary cam member if associated with a pair of contact fingers I2 and II having contact points 52* and 53 respectively. This cam member iii in turn comprises a pair of discs or track members 54 and I! having peripheral cam faces or tracks engaged by the contact fingers I! and 58 respectively.

Each of the component discs 54 and 5! per so I has the identical peripheral shape of track or cam face although in the composite cam member the tracks in their co-operative relationship with respect to each other appear largely shifted or staggered so that they will operate their associated contact fingers in a manner further to be described below. The basic shape of a component disc is shown in Fig. 10'. The peripheral track or disc 54 comprises a raised portion 58 and a complementary depressed portion 51, both portions totalling up to make the circumference. Between the raised and the depressed track portion of disc 54 there is an abrupt step or drop or overhang portion at 58 and a gentle or sloping transition at 58. The peripheral track on the component disc Eli comprises a raised portion ll which is similar to the raised portion 58 on disc 84, and a depressed portion N which is similar to the depressed. portion 5'! on disc 64. Between the raised and the depressed track portion of disc I! there isan abrupt step or drop or overhanging portion at 62, and a gentle or sloping transition at N. I

, As the cam member ll of switch T1 rotates the contact fingers 52 and 53 will assume in the course of an operating cycle a sequence of positions relative to each other which sequence is represented in Figs. 6 to 9. In this way the movements of the contact fingers govern the operation of the electrical control system in timed relation to the brick-pressing cycle.

In Fig. 6 the contact between the fingers 52 and B3 is open due to the open contact points 52 and II, since the tips of the fingers are in contact with identical track levels. of the contact fingers characterizes that period of rotation of the cam member 5| which is herein defined as the rest period R and which is represented by the sum total of the angles a and c in the rotation of the cam member. During this rest period R the open contacts between the fingers I2 and it keep the electrical control system disconnected and free from the influence of the strain gauges and thus un-infiuenced by any strain indications or reactions originating in the sub-frame ii. It will be noted that the angles of rotation a and c of this rest period correspond to the oil-periods a and indicated in the Fig. 11 pressure chart. Points P1 and P2 indicated upon the curve of the chart represent the end and the beginning respectively of the rest period, the period b between points P1 and P2 representing the peak pressure face of the brick-forming cycle.

As the cam member 5! rotates counter-clockwise from the Fig. 6 to the Fig. '7 position in the direction of arrow W, the contact finger 52 because of the step or overhang 58 drops abruptly to the lower level of the depressed track portion 84, while finger it continues upon the raised track portion 80 thus closing the contacts 52' and I3 between the fingers. the contacts corresponds to point P1 in the Fig. 11 chart. The contacts then continue closed while a the cam member ll rotates through an angle 1:

representing what is herein called the alert period of the present control cycle since it places the electrical. control system under the influence of the strain gauges and thus conditions them with respect to strain indications or reactions from the sub-frame ii. The angle b in Fig. '1 corresponds to the alert period or peak pressure period b in the Fig. 11 chart.

, As the cam member 5i continues rotating counter-clockwise, the contact fingers 52 and 53 pass from the Fig. 7 to the Fig. 8 position, that .is from the alert period b they again enter the rest period R. During this phase thefinger 53 because of the step or overhang," of its track drops abruptly from its raised track portion 80 to its depressed track portion ll, thereby opening contacts 52' and 53' between the fingers. as both fingers are now again sliding on even track levels. The opening of the contacts 52' and 53' the sloping transition 59 and onto the raised track portion 58. This merely increases the spread or The open condition The point of closing of fingers 52 and 53 and therefore does not otherwise alter the conditions of the rest period as such.

As soon as the cam member 5i continues rotating counter-clockwise the finger 53 also mounts onto its raised track portion by way of the s.oping transitional portion 83 of its track. This places both fingers again on the identical raised track level in the completion of the cycle.

It will be noted that the component discs or track members 54 and 55 of cam member Bi are mounted upon an outwardly threaded tubular member or sleeve member 84, and that they are pressed face to face towards each other by a pair of nuts 65 and 68 tightened upon the thread of the sleeve member M, a suitable washer or spacer disc 8'! being interposed between the discs 54 and 55. The thus assembled cam member BI is mounted upon the axial horizontal extension ill of the crank shaft 29 (see Fig. 2) to be rotatable therewith.

The operation of the-switch T1 controls and times the predetermined and pro-adjusted alert period b within the press control cycle, during which period this switch establishes merely those connections which condition the electrical control system for response to the strain indications from the sub-frame, without as yet executing the actual moldvolume adjustment. That is to say. the actual operation of the auxiliary motor II to effect themold volume adjustment is governed byswitch Ta which comprises a composite cam member 88 rotating together with cam member 51 of switch T1 and having an associated pair of stationary contact fingers B9 and 10, the cam member 88 and the fingers 69 and 10 as well as the mounting of the cam member 68 upon the shaft extension 50 being structurally similar to those of switch T1.

The function of switch T2 is to actuate the auxiliary motor 48 so as to effectuate mold volume adjustments in satisfying the demand originating from the strain gauges. That demand will be met by switch T: during what is herein called the active control period of the electrical control cycle indicated as hr in the Fig. 11 chart and as angle In in the Fig. 10 showing of the cam member 88. From the Fig. 11 chart it will be seen that this active control period comprises only .a selected and re atively small portion of the peak pressure phase or alert period b, this active control period thus lying well within the limits of the alert period b. Hence the switch T herein also termed the active: control switch, is open or inactive during off-periods a1 and 01 in the Fig. 11 chart, which periods are also designated as angles a1 and 01 on the cam member 88. The showing of active control switch T2 in its Fig. 10 active position should suffice for the understanding of its function since the cyclic operation as such of that switch is in principle similar to cyclic operation of the alerting switch Tl. The difference between switches T1 and Ta does not lie in their individual constructions but in the difference of their timing adjustment, that is the timing adjustment of the component discs or track members with respect to each other in each cam member, and the timing adjustment of the cam members of both switches with respect to each other upon the shaft extension 50. The cam members BI and 68 of both switches are provided with marginal or peripheral calibrations as a guide to their timing adjustment.

(1)) The electrical wiring system The Figs. 4 and 4 wiring diagrams include the R1 supplied to the Wheatstone bridge.

schematic perspective showing of those parts oi the machine which are functionally directly associated with the operation oi the electrical system. Such parts are the sub-frame ii. the mainor crank shaft 28 with its axial extension 88 carrying the cam members it and 88 oi the respective master or timing switches T1 and T2. the contact fingers 82 and 88 of switch T1, the contact fingers 88 and 18 of switch Ts. the auxiliary motor 88 driving the adjusting screw spindle 88 to raise or lower the nut 88 thereon. It will be remembered that this nut has a pair of lugs ll and H to actuate the adjusting lever 88,

which lugs according to this wiringdiagram are utilized to actuate limit switches L1 and L2 insuring stoppage oi the auxiliary motor at upper and lower limits. of travel of the nut 88.

The strain gauges A1, D1, A2, D: as arranged in this wiring diagram represent the resistances or branches oi a Wheatstone bridge W in which strain gauges A1 and D1 join at point ii, strain gauges Di and A: joining at 12, strain gauges A1 and D2 joining at point it, and strain gauges A: and D2 joining by way of a balancing resistance R2 defined by connecting point it and 18 having a movable contact point I8. The bridge circuit proper to furnish the control impulse for the electrical system and eventually for the adjustment oi the brick mold volume, is established across the points II and I8 01' the Wheatstone bridge. An auxiliary current supply for the Wheatstone bridge is furnished by a constant voltage source 17 which is in circuit with a resistance 17 defined by points 18 and I8 and having a slidable contact 88 for adjusting the voltage A conductor 8i leads from point 18 of the voltage source to point I2 of the Wheatstone bridge; a conductor 82 leads from the slidable contact 88 to point I8 of the Wheatstone bridge. A volt meter 88 is connected across the conductors 8| and 82 at points 88 and 88.

The wiring diagram further comprises what is herein called an electronic potentiometer 82" indicated by'the dotted line or box surrounding it. In order to illustrate the principle or its operation this electronic device per se is herein shown in its simplest form by way oi example. The device E comprises an electronic amplifier tube sometimes also called an electronic valve, its principle being that it can control relay circuits through minute impulses or currents or variations 01' potential, derived from a primary source. That is to say, the device E comprises an amplifier tube 88 the elements of which comprise a cathode 81, an anode 88, and a grid 88. During the off-period a and c the grid is under a potential derived through a slidable contact 88 accuses I connected through a conductor III to the -slidable contact 18 of the Wheatstone. bridge W.

is .to say, the switch member I88 is normally closed by spring pressure upon contact I88 maintaining connection between points 82 and 88 of the electronic potentiometer E and points 88 and 88 oithe voltage source 84. If, however, the switch member I88 is in the opposite dot-anddash line position closing upon contact I88, it will thereby connect conductor I88 with the slidable contact I8 of the Wheatstone bridge through the conductor III. A conductor H2 connects point II of the bridge with a point II8 upon conductor 88. Thus may be established the bridge circuit between points 1i and i8 oi the Wheatstone bridge to furnish the control impulse to the electronic potentiometer E and through it the relay current through which the brick mold volume adjustment is realized. l

The relay switch member I88 is normally urged by a spring H4 to close upon contact I88, but

adjustable upon a potentiometer resistance 87 defined as between points or terminals 88 and 88 and in circuit with a constant voltage source 84, for example a No. 6 dry-cell battery. That is to say. one conductor 88 leads from point 88 to a point or terminal 88 oi a control or potentiometer resistance 81 as defined between points 88 and 88', while another conductor I88 leads from point 82 to point I8I oi a relay switch I82 which has a movable switch member I88 and a has an armature H8 surrounded by a solenoid coil II8 having terminals Ill and H8 supplied with operatingcurrent through conductors II! and I28 leading to terminals Ill and II 8 respectively and controlled by a switch herein called the timing switch T1. The details have been described above in view of Figs. 5 to 9. Dot-anddash lines leading from terminals I2I and I22 merely refer to the actual location of switch Ti upon the extension 58 of crank shaft 28 of the press. The closing of the switch Tl. due to the closing upon each other of the normally open fingers 52 and 88 will therefore energize solenoid H8 and the magnetic pull upon armature H8 will overcome the tension of spring I I4 and throw the switch member I88 to release contact I88 while closing upon contact I88.

Reverting now to that portion of the circuit system which is herein termed the electronic potentiometer E, a B-battery I28 supplies auxiliary circuit for the operation of the amplifier tube 88, the battery being in circuit with load resistances H8 and H8 defined by points or terminals 82, I28 and I28, the cathode 81 being connected to point I24 between the two load resistances. The auxiliary tube operating circuit herein also simply called the tube circuit is further defined by a conductor I28 leading to the oneterminal I21 01' a solenoid coil I28, and a conductor I28 leading from the anode 88 to the other terminal =I88 oi solenoid I28. An ammeter I8I is shown in I28 and I28.

The solenoid coil I28 surrounds an armature I88 which is part of a. relay switch I88 which In distinction from the primary relay switch I82 may be called the secondary relay switch having a movable or swingable switch member I81 adapted to close either upon a contact I88 or upon a contact I88. Normally the system is electrically so balanced that the switch member I 88 is maintrined in an intermediate or floating position. However, a control impulse from the strain gauges on subframe I I through the Wheatstone bridge W and through the electronic potentiometer E may cause the switch member i8? to be unbalanced or thrown in either theme or the other direction as the case may be. so as to close upon one of the contacts I88 and I88, which eventually will start the reversible auxiliary motor 46 to rotate in either the one or the other direction to execute the brick mold adjustments called for by the impulses. Thus the secondary relay swtich I36 selectively closes a pair of normally open double-pole motor switch M1 and M2, switch M1 to run the motor in the one direction and switch M2 to run itin the opposite direction. Motor switch M1 is represented by an armature I39 surrounded by a solenoid coil I40 and defined by its terminals HI and I42. The armature I33 actuates switch members I43 and I44 to move in unison and adapted to close upon contacts I45 and I46. Motor switch M2 is represented by an armature I41 surrounded by a solenoid coil I48 defined by its terminals I43 and I50, the armature I41 actuating switch members II and I52 to move in unison and adapted to close upon terminals I53 and I54.

However, the actual closing of the motor switches M1 and M2 is subject to the closing of the master or timing switch T2 indicated in the diagram by its switch member I55 and with terminal I56 and a contact I51. The actual location of the switch T: is indicated by dot-anddash lines leading to the contact fingers 69 and engaging the rotary cam member 68 fixed on the extension 50 of crank shaft 29, the contact fingers 69 and 10 having contacts 69 and 10* adapted to close upon each other but are normally open.

The closing of the motor switches M1 and M2 also requires that the limit switches L1 and L2 be normally closed, limit switch L1 being represented by its switch member I58 with terminal I59 and a contact I60, limit switch L2 being represented by its switch member I6! with terminal I62 and a contact I63. The actual location of these limit switches is indicated for limit switch L1 by dot-and-dash lines leading to a pair of contacts i255; and 160, and for limit switch L2 by dot-and--dash lines leading to a pair of contacts 862 and H13. Thus the limit switches L1 or L2 may he opened by lugs 4i and H respectively depent ang upon whether the nut 38 is moved past its upper or lower limit position on the adjusting St cw spindle 36 by the auxiliary motor 48.

The auxiliary motor 48 is supplied from a power source such as a 110 volt line indicated at I56 comprising the indicators I64 and F64". The motor 53 indicatedby its commutator brushes or contacts i55 and I66 has conductors I61 and I60 leading from these brushes to branch points I69 andxI10 whence a pair of branch conductors HI and I12 lead to switch members I43 and I44 of motor switch M1, and a pair of branch conductors I13 and I14 lead to switch members I5I and I52 of motor switch M2.

The relay switch member I31 is connected with the motor switches M1 and M2 by a conductor I leadingfrom the switch member to terminal I51 of timing switch T2, a conductor I16 leadingfrom switch member $55 of timing switch T2 to a point I11 on the 110 volt conductor i6, a branch conductor {18 leading from a point H9 on conductor I16 to a contact MS of motor switch M1, and a branch conductor i519 leading from point I11 to contact 53 of motor switch M2.

The 110 volt conductor ifid leads to contact I54 of motor switch M2 and has a branch conductor I60 leading to contact M5 of motor switch M1, a sub-branch conductor .IilI leadingfrom point I82 on branch lilfi to terminal I50 of solenoid coil i 18 oter switch M2. A conductor {63 leads from tern lei oi solenoid coil I56 of motor switch M2) to terminal N2 of solenoid OPERATION or THE ELECTRICAL SYSTEM During the rest period R of the operating cycle, when the voltage Ra from dry-cell battery 94 is properly adjusted, and the relay switch member I03 is normally closed upon contact I04 due to the pull of spring II4, there is established a conditioning circuit which will place the grid 69 of tube 86 under such a potential or bias as will permit B-battery current supplied by battery I23 to pass from cathode 81 to anode 88 and through the solenoid 928 of secondary relay switch I36. That is to say, a conditioning circuit is established from point 99, through conductor 95 to point 93, then through potentiometer resistance coil 9! to point 92, through conductor 100 to point or terminal Iiii of the primary relay switch I02,

through switch member i053 to contact point 5%, and through conductor I06 to slidable contact 60. Thus the grid 09 and the cathode B1 are placed under a potential with respect to each other that will keep the secondary relay switch member balanced or floating in neutral position because 0! the tube circuit which includes the B-battery I23, points 92, I20 and E25, balancing resistances H5 and H6, cathode 81, anode 88, conductor I26, solenoid coil H8, and conductor 825.

In order to balance or adjust the system or the controlling potentials in such a manner as to obtain the desired action of the relay switch i001, one may proceed as follows:

First the grid potentiometer P or grid poten tiai R1; is so adjusted that the relay switch member 531 closes properly upon either the contact I36 or the contact 036, whichever the case may be, in response to impulses from the responsive strain gauges A1 and A2. The demand from these strain gauges causes an unbalance of the Wheatstone bridge W which reaches the relay cir cuit passing through electronic tube We in case the bridge circuit or potential is thrown onto the tube by way of the primary relay switch member )3 closed upon the contact M35.

When the responsive strain gauges A1 and A2 are not subjected to deformations from any strains in sub-frame ii, that condition will leave the Wheatstone bridge circuit balanced, that is all iour branches or resistances as represented by the strain gauges A1, D1, A2, D2, are in a desired balance, so that the bridge terminals 15 and 16 have a suitable and desired potential between them. This potential is such that when coupled with the tube circuit it will not affect the tube circuit and hence will not affect the secondary relay switch ltd unless disturbed or changed by peak brick-forming pressures which are either higher or lower than a desired intermediate value and which therefore unbalance the Wheatstone bridge by a corresponding change in the resist ance value of the responsive strain gauges A1 and As.

That is, when the resistance value of the strain gauges A1 and A: is lower and that oi the strain gauges D1 and D3 is higher than the desired in= asses termediate value, it will cause the secondary relay switch member I31 to close upon one of its contacts, say contact I38 and thereby potentially energize solenoid I40 ot'motor switch M1 to close the same, that is provided switch T: is closed, This starts the auxiliary motor 48 to run in the corresponding direction whereby it raises the nut 38 through rotation of the spindle 38 thereby lowering the outer end 43 of adjusting lever 38 engaging cross bar 44, and thereby ultimately effecting a downward adjustment of the bottom plunger l8 equivalent to a compensatory increase of the effective mold volume receiving the brick-forming mixture.

correspondingly, when the resistance value of the responsive strain gauges A1 and A1 is higher and that of the strain gauges D1 and D1 is lower than the desired intermediate value, it will cause the secondary relay switch member I31 to close upon the other contact I30 and thereby potentiallyenergize solenoid I48 of motor switch M2 to close the same, that is provided switch T2 is closed. This starts the auxiliary motor 48 to run in the opposite direction whereby it lowers the nut 38 through rotation of the'spindle 38, thereby raising the outer end 43 of adjusting lever 38 engaging cross bar 44, and thereby ultimately eflecting an upward adjustment of the bottom plunger I8 equivalent to a compensatory decrease of the eflective mold volume receiving the brickforming mixture. Within the Wheatstone bridge W the responsive strain gauges A1 and A: are in balance against switch T1 and eifectuating the operation of auxiliary motor 48 by energizing the solenoid I40 of motor switch M1. That is, from point I11 on the power line I84 a circuit is established through conductor I18, closedtiming switch T1,.

. conductor I18, terminal I31, switch member I31,

contact I38','conductor I88, through normally closed limit switch L2, conductor I81, solenoid coil the non-responsive strain gauges D1 and D1, but

inasmuch as all four strain gauges are subjected to the identical temperature fluctuation and the attendant resistance changes, it will be seen that these resistance .changes and any errors flowing from such changes with respect to strain gauge indications are cancelled out or compensated for by the very arrangement of the four strain gauges within the Wheatstone bridge. Hence the indications or impulses from theresponsive strain gauges A1 and A: will be transmitted through the Wheatstone bridge undistorted by whatever resistance changes the responsive strain gauges'A1 and A: per se may undergo because of temperature changes.

In the course of its brick-forming cycle the machine passes from the rest period R into the alerting period b as the crank shaft 28 rotates the cam member 8i of timing switch T1 to close contacts 82 on 83 of contact fingers 82 and 83, thus energizing solenoid III of the primary relay switch I02 to throw switch member I03 against the pull of spring H4 into the dotted line position in which it closes upon contact I 05. This couples the bridge circuit of the Wheatstone bridge W- with the tube circuit, in that point 83 of the electronic potentiometer E is new connected to point ll of the Wheatstone bridge by way of conductor II2, point H3, and conductor 85, and point 82 of the electronic potentiometer E connected to point 18 of the Wheatstone bridge by way of conductor III, contact I08, switch member I03, terminal IN, and conductor I00. This condition maintains while the cam member of timing switch T1 moves through the alerting period atthe end of which solenoid H8 is deenergized due to the breaking of the contacts 8t and 53 01' the contact fingers 82 and 83, which allows spring H4 to return the switch member I03 to its normal closing position upon contact I08.

Let it be assumed that during the alerting motor switch M1.

I40, conductor I83, point I80, conductor I8I, point I82, and conductor I to a point on power line I84. This closes the normally openmotor switch M1 to close a power feeding circuit to motor 48 from the power line I84, through conductor I18, point I18, conductor I18, contact I48, switch member I43, conductor I", point I10, conductor I81, and contact brush I88 through the motor armature, to contact brush I88, conductor I88, point I88, conductor I12, switch member I44, contact I48, and conductor I80 to a point on the power line I84 Alternatively it may be assumed that during the alerting period b the demand from the strain gauges has caused the secondary relayswitch member I31 to close-upon contact I38 and to remain closed for the duration of that period. Within that period, the rotation of crank-shaft 28 and of cam member 88 reaching point Q1 of the pressure-time diagram (Fig. 11) enters the active control period in as cam member 88 closes the timing switch T2, energizing the solenoid coil I48 oi motor switch M2 and closing'the same eflectuating the operation of auxiliary motor 48 to run in a direction opposite to the direction that was previously assumed in response to the closing of That is, from point I11 on power line I84 a circuit is established through conductor I 18, closed timing switch T2, conductor I15, terminal I31, switch member I31, contact I38, conductor I34, closed limit switch L1, conductor I85, solenoid coil I48, point I50, conductor IBI, point I82, and conductor I80 to a point on power line I84 This circuit closes the normally open motor switch m to close a power feed circuit to the auxiliary motor 48 from power line I84 to contact point I83, closed switch member I5I, conductor I13, point I89, conductor I88, contact brush I88, through the motor armature to contact brush I 88, returning through conductor 881, point I10, conductor I14, and closed switch member I52 to'a point I84 on the power line I64".

When in the course of the operating cycle the rotation of crank-shaft 28 and hence of the cam member 88 reaches the point Q2 of the pressuretime diagram (Fig. 11), the timing switch T2 opens marking the end of the active control period b1. That is, at that point the cam member 88 allows the contacts 68 and 10 on contact fingers 89 and 10 to open, thus de-energizing whichever of the motor switches M1 or Mz might have been operating to make a compensatory mold volume adjustment, and concluding the active control period b1..

Shortly thereafter, as the rotation of crankshaft 29 and hence of cam member ii of timing 21 switch T1 reaches P2 of the pressure-time diagram (Fig. 11 the timing switch T2 also opens tie-energizing solenoid coil I iii of the primary relay switch I02, allowing spring H4 to return the switch member M3 to its closing position upon contact HM, thus restoring the electrical system to the balanced condition of the rest period R. which influences the solenoid coil I28 in such a manner as to allow the secondary relay switch member I31 to release whichever of the contacts "8 and I39 it may have held engaged, and to return to its neutral or balanced or floating position which in turn is the result orthe timing of the circuit derived from the auxiliary constant voltage source or No. 6 dry-cell battery 9 and initially described in the operation of this cycle.

If for any reason the corrective upward or downward movements of the adjusting nut 38 exceed a predetermined upper or lower limit, the lugs H or 4! will open limit switch L1 or In respectively so as to open motor switch M2 or Mr respectively, thus stopping any further movement of the nut 38.

As for the function of the electronic potentiometer E it will be understood that, if the bridge output or potential at points H and T6 of the Wheatstone bridge increases because of excessive brick-forming or peak pressure due to an increase in the apparent density of the feed mixture, and a corresponding reaction of the strain gauges, the grid 98 becomes more negative thus permitting less B-battery current to pass through the amplifier tube 85. This in turn causes the solenoid 128 of the secondary relay switch ME to be less energized, thus releasing the armature 435 to the extent that it closes the switch member 13? upon contact I33 thereby conditioning motor switch M1. That is, the

' motor circuit is thus conditioned to start the motor it) to run in the corresponding direction upon closing of the timing switch T2, to effect the required compensatory mold .volume adjust:- ment whereby the bottom plunger i9 is adjusted upwardly.

Similarly, if the brick-forming or peak-pressure is reduced below the desired value due to a decrease in the apparent density of the feed mixture and a corresponding reaction of the strain gauges, thus changing the bridge output or potential at points ii and i of the Wheatstone bridge, that change of potential impressed upon the grid 98 will render the grid less negative and therefore permit more E-supply current to pass through tube 38. This increased current energizes the solenoid i S of secondary relay switch 13% to the extent'that it will pick up the armature lfifi causing the switch member l3? to close upon contact 138 thus conditioning motor switch M2. That is the motor circuit is thus conditioned to start the motor 58 to run in the opposite direction upon closing of the timing switch T2, to effect the required compensatory mold volume adjustment whereby the bottom plunger i9 is adjusted downwardly.

In either case, whether the demand be for upward or for downward adjustment of the bottom plunger it, the control operation may continue by increments through a sequence of brick-forming cycles until the full total of required bottom plunger adjustment is reached, that is until the demand from the strain gauges is satisfied.

After the full measure of the required adjustment has been reached, then in the subsequent brichiorniing cycles the switch member 43? will remain in its floating or neutral position. That is even though the masteror timing switches T1 and T: will function in each cycle in the man ner described above, there will be no control response as the control switches M1 and M2 will not be ailected and will not respond.

With a knowledge of circuit constants, the actual voltage indicated by M2 (or current indicated by Hi) may be calculated for any given strain measured by the gauges. Through a knowledge of mechanics and the design of the press this strain can be converted to specific pressure units. Thus voltmeter H2 or ammeter i3! can be provided with an auxiliary scale from which the'actual pressing pressure may be read directly. By varying R1 the sensitivity of the bridge circuit W may be varied so that this scale will always be correct, no matter what pressing area is being used.

Adjustment for operation of the electrical system involvingthe dry cell 5J4, constant voltage source i'l, strain-gauge bridge circuit W, and electronic potentiometer E, may be effected as follows:

a. With potentiometer resistance ill in the circuit adjust W to provide a voltage, indicated by 83, which will cause H132 to read directly in pounds per square inch for whatever total pressing area is being. used.

b. With no load on the press, and with switch member i533 contacting Hid, adjust sliding contact Gil until it coincides with point 99, i. e. a voltage of zero will then be applied to the tube circuit. Then adjust R until :32 indicates zero pounds per square inch pressing pressure.

0. With the press loaded exactly to the desired control point, and with switch member its contacting Hi5, adjust R2 until switch I36 is in the neutral position (2. With switch member liiii contacting led, adjust sliding contact until switch member i3? is again in the neutral position.

The use of the two pairs of strain gauges. their mounting on the sub-frame of the machine and the manner of their operation as shown in the present embodiment has certain advantages un= der certain conditions. That is, with a responsive strain gauge mounted on each arm, the pressure average taken across the several mold boxes is obtained. Furthermore, by mounting the nonresponsive strain gauges as close as possible to the responsive strain gauges and by connecting them into the bridge circuit W in the manner shown, all gauges are subjected to identical temperature conditions or fluctuations so that errors due to temperature influence from that angle are con celled out.

Other modes of using and mounting strain gauges .are possible within the scope of this vention. For example, the non-responsive strain gauges may be mounted separately from the responsive strain gauges and separately from the sub-frame H, as long as the temperature conditions to which they are subjected are the same as those which the responsive strain gauges must encounter.

Also, the control could be made to operate with only a single responsive strain gauge mounted on. the press.

As to the scope of the concept of this invention, it will be understood that the circuit controlled by the primary relayswitch H32 to establish the rest period a-l-c" which circuit may also be termed the holding circuit, is a, refinement upon a more basic concept, the more basic concept be- 23 log directed to the actual adjustments or control phases b and/or bi proper.

No undue limitation should be imposed upon the scope of this invention in view of the Wheatstone bridge circuit disclosed in the present embodiment. That is to say, other than the specific Wheatstone bridge circuit may be employed. Thus the bridge circuit may be described more broadly as a basically four-branch potential balancing bridge circuit in which at least one branch includes a responsive strain gauge.

Still another consideration regarding the scope of this invention is that not only resistances, but also reactances, or capacitances may constitute branches of the potential-balancing circuit which by way of example only is herein presented as a Wheatstone bridge that is based on the use of resistanbe type branches. For example also, electronic tubes may be embodied in or may represent one or more branches of such a balancing circuit. Accordingly also, other than resistance type strain gauges, for example capacitance or reactance type strain gauges may be employed within the scope of this invention and depending upon conditions alternating current may be em ployed instead of direct current auxiliary current sources shown in the present embodiment.

What we claim is:

1. The combination with a cyclically operating power-driven brick-press having a stationary main frame, a brick mold stationary with said frame, a vertical sub-frame vertically movable upon and with respect to the stationary main frame in a manner controlled by a brick-forming cycle which sub-frame is adapted to absorb directly the brickforming peak pressure, a top plunger and a bottom plunger for the mold and carried by said sub-frame, mechanisms for actuating the plungers with respect to each other and with respect to the mold to eflect a brick-forming and -eiecting cycle, controllable adjusting means having a rotatable adjusting element for upwardly or downwardly adjusting the initial position of the bottom plunger determining the effective mold volume receiving the brick-forming mixture, and a reversible motor for driving said rotatable adjusting element; of a control system for automatically eiiecting an upward adjustment of the bottom plunger responsive to an increase in the apparent density of the brick-forming mixture and for effecting a downward adjustment of the bottom plunger responsive to a decrease in the apparent density .of the mixture which system comprLses a pair of responsive strain gauges mounted upon the peak pressure-absorbing portion of the sub-frame, a pair of non-responsive strain gauges subjected to substantially the same temperature conditions as the responsive strain gauges, a four-branch potential-balancing circuit with adjustable constant voltage supply to furnish input potential for the circuit, both said pairs of strain gauges constituting respective pairs of branch resistances of the circuit, the pair of responsiye strain gauges being adapted to alter the bridge output potential when subjected to strain while temperature influences upon the strain gauges cancel out because of the balance condition between the responsive and the non-respom sive strain gauges within the circuit, an auxiliary electronic circuit variable in response to variations oi the bridge output potential, means for impressing said bridge output potential upon said electronic circuit, motor relay means controlled by said electronic circuit and adapted to close a motor-operating circuit to run the motor in one 24 a direction responsive to a drop of the bridge potential below a given intermediate value and to run the motor in the opposite direction responsive to a rise of the bridge output potential above a given intermediate value, and means for limiting the I bridge output, and timing means controlled by" the press cycle to thus selectively actuate the relay means in synchronism with a press cycle to impress said bridge output potential during a peak pressure portion of the cycle.

4. A control system according to claim 1, with the addition of an auxiliary adjustable constant voltage supply, primary relay means operable by a primary power source for selectively impressing upon said electronic circuit either the potential of the auxiliary voltage during an alerting period of a press cycle or the bridge output potential during a rest period of the press cycle, a timing switch controlling said primary power source for thus selectively actuating said relay means, and timing means controlled by the press cycle to actuate said timing switch in synchronism with a press cycle whereby said alerting period comprises a peak pressure portion of the cycle.

5. A control system according to claim 1', with the addition of a timing switch controlling said motor operating circuit, and timing means controlled by the press cycle for actuating said switch to run said motor during an active control period comprising a peak pressure portion of a press for actuating said timing switches in synchronism with said press cycle so that the alerting period comprises a peak pressure portion of the cycle and the active control period comprises a smaller peak pressure portion within the first mentioned peak pressure portion.

LA control system according to claim 1, in which the press-actuating means comprise a stationary crank-shaft one rotation of which moves the top plunger through a full reciprocation, with the addition of an auxiliary adjustable constant voltage supply. primary relay means operable by a primary electric power source and selectively operable thereby to impress upon said electronic circuit either the potential of said auxiliary voltage supply during an alerting period or the bridge output potential during a rest period, a first timing switch controlling said primary power source for thus selectively actuating said relay means. a second timing-switch controlling said motoroperating circuit to run the motor during an 9.0-

25 tive control period, and timing means effective between said crank shaft and said timing switches for actuating said timing switches in synchronism with a press cycle so that said alerting period comprises a peak pressure portion of the cycle and said active control period comprises a peak pressure portion within said first-mentioned peak pressure portion. I

8. A control system according to claim 1, in which one responsive strain gauge is disposed on each side of the sub-frame.

9. A control system according to claim 1, in which one responsive as well as one non-responsive strain gauge is disposed on each side of the sub-frame.

10. A control system according to claim 1, in which the non-responsive strain gauges are mounted upon the sub-frame.

11. A control system according to claim 1, with the addition of an auxiliary adjustable constant voltage supply, primary relay means operable by a primary electric power source for selectively impressing upon the electronic circuit either the potential of said auxiliary voltage supply during a rest period or the bridge output potential during an alerting period, a first timing switch controlling said primary power source for thus selectively actuating said relay means, a second timing switch controlling said motor operating circuit to run the motor during an active control period, timing means controlled by the press cycle for actuating said timing switches in synchronism with said press cycle so that the alerting period comprises a peak pressure portion of the cycle and the active control period comprises a smaller peak pressure portion within the first-mentioned peak pressure portion, in which system one of said switches comprises a rotatable switch member having a pair of component cam members rotatable as a unit each provided with a peripheral track having a relatively raised and a relatively recessed peripheral portion, means for angularly adjusting said component cam members with respect to each other whereby the track portions said component cam members are staggered relative to one another, a pair of contact fingers each of which engages a respective track, the angular adjustment of the tracks relative to each other being such as to open and to close the contact fingers with respect to each other at predetermined points of rotation of said switch member.

12. A control system according to claim 1, with the addition of an auxiliary adjustable constant voltage supply, primary relay means operable by a primary electric power source for selectively impressing upon the electronic circuit either the potential of said auxiliary voltage supply during alrest period or the bridge output potential during an alerting period, a, first timing switch controlling said primary power source for thus selectively actuating said relay means, a second timing switch controlling said motor-operating circuit to run the motor during an active control period, timing means controlled by the press cycle for actuating said timing switches in synchronism with said press cycle so that the alerting period comprises a peak pressure portion of the cycle and the active control period comprises a smaller peak pressure portion within the firstmentioned peak pressure portion, in which system one of said switches comprises a rotatable switch member having a pair of component cam members rotatable as a unit each provided with a peripheral track having a relatively raised and a relatively recessed peripheral portion, means for angularly adjusting said component members with respect to each other whereby the track portions of said component cam members are staggered relative to one another, and a pair of contact fingers each of which engages a respective track, the angular adjustment of the tracks relative to each other being such as to open' and to REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,256,798 Yeakel Sept. 23, 1941 Gates Aug. 25, 1942 

